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An Update to 6LoWPAN NDCisco Systems, IncSophia AntipolisFRANCEpthubert@cisco.comSanta Clara, CAUSAnordmark@sonic.netSan Jose, CAUSAsamitac.ietf@gmail.comInternet
6lo
This specification updates RFC 6775 - 6LoWPAN Neighbor Discovery,
to clarify the role of the protocol as a registration technique,
simplify the registration operation in 6LoWPAN routers, and
provide enhancements to the registration capabilities, in particular
for the registration to a Backbone Router for proxy ND operations.
RFC 6775, the "Neighbor Discovery Optimization for
IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs)"
introduced a proactive registration mechanism to IPv6 Neighbor Discovery
(ND) services that is well suited to nodes belonging to a Low Power Lossy
Network (LLN).
The scope of this draft is an IPv6 LLN,
which can be a simple star or a more complex mesh topology.
The LLN may be anchored at an IPv6 Backbone Router (6BBR)
.
This specification modifies and extends the behavior and protocol
elements of RFC 6775 to enable additional
capabilities, in particular the registration to a 6BBR for proxy ND
operations.
The purpose of the Address Registration Option (ARO)
and of the Extended ARO (EARO) that is introduced in this document is to
facilitate duplicate address detection (DAD) for hosts and pre-populate
Neighbor Cache Entries (NCE) in the routers to
reduce the need for sending multicast neighbor solicitations and also to be
able to support IPv6 Backbone Routers.
In some cases the address registration can fail or be useless for reasons
other than a duplicate address.
Examples are the router having run out of space, a registration bearing a
stale sequence number (e.g. denoting a movement of the host after this
registration was placed), a host misbehaving and attempting to register an
invalid address such as the unspecified address , or
the host using an address which is not topologically correct on that link.
In such cases the host will receive an error to help diagnose the issue and
may retry, possibly with a different address, and possibly registering to a
different 6LR, depending on the returned error.
However, the ability to return errors to address registrations MUST NOT be
used to restrict the ability of hosts to form and use addresses as recommended
in "Host Address Availability Recommendations".
In particular, this is needed for enhanced privacy, which implies that each
host will register a multiplicity of address as part mechanisms like
"Privacy Extensions for Stateless Address
Autoconfiguration (SLAAC) in IPv6".
This implies that the capabilities of 6LR and 6LBRs in terms of number of
registrations must be clearly announced in the router documentation, and
that a network administrator should deploy adapted 6LR/6LBRs to support the
number and type of devices in his network, based on the number of IPv6
addresses that those devices require.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL",
"SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
and "OPTIONAL" in this document are to be interpreted as
described in RFC 2119.
Readers are expected to be familiar with all the terms and concepts
that are discussed in
"Neighbor Discovery for
IP version 6",
"IPv6 Stateless Address
Autoconfiguration",
"IPv6 over Low-Power
Wireless Personal Area Networks (6LoWPANs): Overview, Assumptions,
Problem Statement, and Goals",
"Neighbor Discovery Optimization
for Low-power and Lossy Networks" and
"Multi-link Subnet Support in IPv6".
Additionally, this document uses terminology from
"Terms Used in Routing for Low-Power and Lossy Networks"
and
the
"6TiSCH Terminology",
as well as this additional terminology:
This is an IPv6 transit link that interconnects 2 or more Backbone
Routers. It is expected to be deployed as a high speed Backbone in order
to federate a potentially large set of LLNS. Also referred to as a
LLN Backbone or Backbone network.
An IPv6 router that federates the LLN using a Backbone link as a Backbone.
A 6BBR acts as a 6LoWPAN Border Routers (6LBR) and an Energy Aware Default
Router (NEAR).
This is the aggregation of multiple LLNs as defined in
RFC 4919, interconnected
by a Backbone Link via Backbone Routers, and forming a single IPv6
MultiLink Subnet.
The process during which a wireless Node registers its address(es) with
the Border Router so the 6BBR can proxy ND for it over the Backbone.
The state in the 6BBR that associates an IP address with a MAC address,
a port and some other information about the node that owns the IP
address.
The node for which the registration is performed, which owns the fields
in the EARO option.
The node that performs the registration to the 6BBR, either for one of
its own addresses, in which case it is Registered Node and indicates its
own MAC Address as Source Link Layer Address (SLLA) in the NS(EARO),
or on behalf of a Registered Node that is reachable over a LLN mesh.
In the latter case, if the Registered Node is reachable from the 6BBR
over a Mesh-Under mesh, the Registering Node indicates the MAC Address of
the Registered Node as SLLA in the NS(EARO).
Otherwise, it is expected that the Registered Device is reachable over a
Route-Over mesh from the Registering Node, in which case the SLLA in the
NS(ARO) is that of the Registering Node, which causes it to attract the
packets from the 6BBR to the Registered Node and route them over the LLN.
The address owned by the Registered Node node that is being registered.
This specification extends the Address Registration Option (ARO) defined
in RFC 6775; in particular a "T" flag is
added that must be set is NS messages when this specification is used,
and echo'ed in NA messages to confirm that the protocol effectively
supported.
Support for this specification can thus be inferred from the presence of
the Extended ARO ("T" flag set) in ND messages.
In order to support various types of link layers, this specification also
adds recommendation to allow multiple registrations, including for privacy
/ temporary addresses, and provides new mechanisms to help clean up stale
registration states as soon as possible.
A Registering Node that
supports this specification will favor registering to a 6LR that indicates
support for this specification over that of RFC 6775.
This specification extends the ARO option that is used for
the process of address registration. The new ARO is referred to as
Extended ARO (EARO), and its semantics are modified as follows:
The address that is being registered with a Neighbor Solicitation (NS)
with an EARO is now the Target Address, as opposed to the Source Address
as specified in RFC 6775
(see for more).
This change enables a 6LBR to use an address of his as source to the
proxy-registration of an address that belongs to a LLN Node to a 6BBR.
This also limits the use of an address as source address before it is
registered and the associated Duplicate Address Detection (DAD) is
complete.
The Unique ID in the EARO option does no more have to be a MAC address
(see for more).
This enables in particular the use of a Provable Temporary UID
(PT-UID) as opposed to burn-in MAC address, the PT-UID providing a trusted
anchor by the 6LR and 6LBR to protect the state associated to the node.
The specification introduces a Transaction ID (TID) field in the EARO
(see for more on TID).
The TID MUST be provided by a node that supports this specification and a
new T flag MUST be set to indicate so. The T bit can be used to determine
whether the peer supports this specification.
Finally, this specification introduces a number of new Status codes to
help diagnose the cause of a registration failure
(more in ).
The specification expects that the Registered Node can provide
a sequence number called Transaction ID (TID) that is incremented with
each re-registration.
The TID essentially obeys the same rules as the Path Sequence field in
the Transit Information Option (TIO) found in the RPL Destination
Advertisement Object (DAO) . This way, the
LLN node can use the same counter for ND and RPL, and a 6LBR
acting as RPL root may easily maintain the registration on behalf of a
RPL node deep inside the mesh by simply using the RPL TIO Path Sequence
as TID for EARO.
When a Registered Node is registered to multiple BBRs in parallel, it is
expected that the same TID is used, to enable the 6BBRs to correlate the
registrations as being a single one, and differentiate that situation from
a movement.
If the TIDs are different, a conflict resolution inherited from
RPL sorts out the most recent registration and other
ones are removed.
The operation for computing and comparing the Path Sequence is detailed in
section 7 of RFC 6550 and applies to the TID
in the exact same fashion.
The resolution is used to determine the freshest registration for a
particular address, and an EARO is processed only if it is the freshest,
otherwise a Status code 3 "Moved" is returned.
The Owner Unique ID (OUID) enables to differentiate a real duplicate
address registration from a double registration or a movement.
An ND message from the 6BBR over the Backbone that
is proxied on behalf of a Registered Node must carry the most recent EARO
option seen for that node. A NS/NA with an EARO and a NS/NA without a EARO
thus represent different nodes and if they relate to a same target then
they reflect an address duplication.
The Owner Unique ID can be as simple as a EUI-64 burn-in address, if
duplicate EUI-64 addresses are avoided.
Alternatively, the unique ID can be a cryptographic string that can can be
used to prove the ownership of the registration as discussed in
"Address Protected Neighbor Discovery for Low-power and Lossy Networks"
.
In any fashion, it is recommended that the node stores the unique Id or
the keys used to generate that ID in persistent memory.
Otherwise, it will be prevented to re-register after a reboot that would
cause a loss of memory until the Backbone Router times out the registration.
This specification changes the behavior of the 6LN and the 6LR so that the
Registered Address is found in the Target Address field of the NS and NA
messages as opposed to the Source Address.
The reason for this change is to enable proxy-registrations on behalf of
other nodes in Route-Over meshes, for instance to enable that a RPL root
registers addresses on behalf LLN nodes that are deeper in a 6TiSCH mesh,
as discussed in .
In that case, the Registering Node MUST indicate its own address as source
of the ND message and its MAC address in the Source Link-Layer Address
Option (SLLAO), since it still expects to get the packets and route them
down the mesh.
But the Registered Address belongs to another node, the Registered Node,
and that address is indicated in the Target Address field of the NS
message.
With this convention, a TLLA option indicates the link-layer address
of the 6LN that owns the address, whereas the SLLA Option in a NS message
indicates that of the Registering Node, which can be the owner device,
or a proxy.
Since the Registering Node is the one that has reachability with the 6LR,
and is the one expecting packets for the 6LN, it makes sense to maintain
compatibility with RFC 6775, and it is REQUIRED that
an SLLA Option is always placed in a registration NS(EARO) message.
Considering that LLN nodes are often not wired and may move, there is no
guarantee that a Link-Local address stays unique between a potentially variable
and unbounded set of neighboring nodes. Compared to RFC 6775,
this specification only requires that a Link-Local address is unique
from the perspective of the peering nodes. This simplifies the Duplicate Address
Detection (DAD) for Link-Local addresses, and there is no DAR/DAC exchange between
the 6LR and a 6LBR for Link-Local addresses.
Additionally, RFC 6775 requires that a 6LoWPAN Node (6LN)
uses an address being registered as the source of the registration message.
This generates complexities in the 6LR to be able to cope with a potential
duplication, in particular for global addresses. To simplify this,
a 6LN and a 6LR that conform this specification always use
Link-Local addresses as source and destination addresses for
the registration NS/NA exchange. As a result, the registration
is globally faster, and some of the complexity is removed.
In more details:
An exchange between two nodes using Link-Local addresses implies that they
are reachable over one hop and that at least one of the 2 nodes acts as a
6LR. A node MUST register a Link-Local address to a 6LR in order to obtain
reachability from that 6LR beyond the current exchange, and in
particular to use the Link-Local address as source address to register
other addresses, e.g. global addresses.
If there is no collision with
an address previously registered to this 6LR by another 6LN, then,
from the standpoint of this 6LR, this Link-Local address is unique and
the registration is acceptable. Conversely, it may possibly happen that
two different 6LRs expose a same Link-Local address but different link-layer
addresses. In that case, a 6LN may only interact with one of the
6LR so as to avoid confusion in the 6LN neighbor cache.
The DAD process between the 6LR and a 6LoWPAN Border Router (6LBR),
which is based on a Duplicate Address Request (DAR) /
Duplicate Address Confirmation (DAC) exchange as
described in RFC 6775, does not need to take
place for Link-Local addresses.
It is desired that a 6LR does not need to modify its state associated to
the Source Address of an NS(EARO) message. For that reason, when possible,
it is RECOMMENDED to use an address that is already registered with a 6LR
When registering to a 6LR that conforms this specification, a node
MUST use a Link-Local address as the source address of the registration,
whatever the type of IPv6 address that is being registered.
That Link-Local Address MUST be either already registered, or the
address that is being registered.
When a Registering Node does not have an already-Registered Address,
it MUST register a Link-Local address, using it as both the Source and the
Target Address of an NS(EARO) message. In that case, it is RECOMMENDED to
use a Link-Local address that is (expected to be) globally unique, e.g.
derived from a burn-in MAC address.
An EARO option in the response NA indicates that the 6LR supports this
specification.
Since there is no DAR/DAC exchange for Link-Local addresses, the 6LR may
answer immediately to the registration of a Link-Local address, based
solely on its existing state and the Source Link-Layer Option that MUST
be placed in the NS(EARO) message as required in RFC 6775.
A node needs to register its IPv6 Global Unicast IPv6 Addresses (GUA) to a
6LR in order to obtain a global reachability for these addresses via that
6LR. As opposed to a node that complies to RFC 6775, a
Registering Node registering a GUA does not use that GUA as Source Address
for the registration to a 6LR that conforms this specification. The
DAR/DAC exchange MUST take place for non-Link-Local addresses as
prescribed by RFC 6775.
This section discusses protocol actions that involve the Registering Node,
the 6LR and the 6LBR. It must be noted that the portion that deals with a
6LBR only applies to those addresses that are registered to it, which, as
discussed in , is not the case for Link-Local
addresses.
The registration state includes all data that is stored in the router
relative to that registration, in particular, but not limited to, an NCE
in a 6LR. 6LBRs and 6BBRs may store additional registration information
in more complex data structures and use protocols that are out of scope
of this document to keep them synchonized when they are distributed.
When its Neighbor Cache is full, a 6LR cannot accept a new registration.
In that situation, the EARO is returned in a NA message with a Status of 2,
and the Registering Node may attempt to register to another 6LR.
Conversely the registry in the 6LBR may be saturated, in which case the
6LBR cannot guarantee that a new address is effectively not a duplicate.
In that case, the 6LBR replies to a DAR message with a DAC message that
carries a Status code 9 indicating "6LBR Registry saturated", and the
address stays in TENTATIVE state.
A node renews an existing registration by repeatedly sending NS(EARO)
messages for the Registered Address. In order to refresh the registration
state in the 6LBR, these registrations MUST be reported to the 6LBR.
This is normally done through a DAR/DAC exchange, but the refresh MAY
alternatively be piggy-backed in another protocol such as RPL
, as long as the semantics of the EARO are fully
carried in the alternate protocol.
In the particular case of RPL, the TID MUST be used as the Path
Sequence in the TIO, and the Registration Lifetime MUST be used
as Path Lifetime. It is also REQUIRED that the root of the RPL DODAG
passes that information to the 6LBR on behalf of the 6LR, either through
a DAR/DAC exchange, or through internal methods if they are collocated.
A node that ceases to use an address SHOULD attempt to deregister that
address from all the 6LRs to which it has registered the address, which
is achieved using an NS(EARO) message with a Registration Lifetime of 0.
A node that moves away from a particular 6LR SHOULD attempt to
deregister all of its addresses registered to that 6LR.
Upon receiving a NS(EARO) message with a Registration Lifetime of 0 and
determining that this EARO is the freshest for a given NCE
(see ), a 6LR cleans up its NCE.
If the address was registered to the 6LBR, then the 6LR MUST report to
the 6LBR, through a DAR/DAC exchange with the 6LBR, or an alternate
protocol, indicating the null Registration Lifetime and the latest TID
that this 6LR is aware of.
Upon the DAR message, the 6LBR evaluates if this is the freshest EARO it
has received for that particular registry entry. If it is, then the entry
is scheduled to be removed, and the DAR is answered with a DAC message
bearing a Status of 0 "Success". If it is not the freshest, then a Status
2 "Moved" is returned instead, and the existing entry is conserved.
The 6LBR SHOULD conserve the address in a DELAY state for a configurable
period of time, so as to protect a mobile node that deregistered from one
6LR and did not register yet to a new one.
RFC 7400 introduces the 6LoWPAN Capability
Indication Option (6CIO) to indicate a node's capabilities to its peers.
This specification extends the format defined in RFC 7400 to signal the
support for EARO, as well as the capability to act as a 6LR, 6LBR and 6BBR.
With RFC 7400, the 6CIO is typically sent
Router Solicitation (RS) messages.
When used to signal the capabilities above per this specification, the 6CIO
is typically present Router Advertisement (RA) messages but can also be
present in RS, Neighbor Solicitation (NS) and Neighbor Advertisement (NA)
messages.
This specification does not introduce new options, but it modifies existing
ones and updates the associated behaviors as follow:
The Enhanced Address Registration Option (EARO) is intended to be used
as a replacement to the ARO option within Neighbor Discovery NS and NA
messages between a LLN node and its 6LoWPAN Router (6LR), as well
as in Duplicate Address Request (DAR) and the Duplicate Address
Confirmation (DAC) messages between 6LRs and 6LBRs in LLNs meshes such
as 6TiSCH networks.
An NS message with an EARO option is a registration if and only if it
also carries an SLLAO option.
The AERO option also used in NS and NA messages between Backbone Routers
over the Backbone link to sort out the distributed registration state,
and in that case, it does not carry the SLLAO option and is not confused
with a registration.
The EARO extends the ARO and is recognized by the "T" flag set.
When using the EARO option, the address being registered
is found in the Target Address field of the NS and NA messages.
This differs from 6LoWPAN ND RFC 6775
which specifies that the address being registered is the source of the NS.
The format of the EARO option is as follows:
Option Fields
33
8-bit unsigned integer.
8-bit unsigned integer. Indicates the status
of a registration in the NA response. MUST
be set to 0 in NS messages. See
below.This field is unused. It MUST be initialized to zero by
the sender and MUST be ignored by the receiver.
One bit flag. Set if the next octet is a used as a TID.
1-byte integer; a transaction id that is maintained by the node
and incremented with each transaction.
it is recommended that the node maintains the TID in a persistent storage.
16-bit integer; expressed in minutes.
0 means that the registration has ended and the associated state should
be removed.
A globally unique identifier for
the node associated. This can be the EUI-64 derived IID of an interface,
or some provable ID obtained cryptographically.
ValueDescription 0..2See RFC 6775.
Note that a Status of 1 "Duplicate Address" applies to the Registered
Address. If the Source Address conflicts with an existing registration,
"Duplicate Source Address" should be used.3Moved: The registration fails because it is not the freshest.
This Status indicates that the registration is rejected because another
more recent registration was done, as indicated by a same OUI and a more
recent TID. One possible cause is a stale registration that has
progressed slowly in the network and was passed by a more recent one.
It could also indicate a OUI collision.4Removed: The binding state was removed. This may be placed in an
asynchronous NS(ARO) message, or as the rejection of a proxy
registration to a Backbone Router5Proof requested: The Registering Node is challenged for owning
the Registered Address or for being an acceptable proxy for the
registration.
This Status is expected in asynchronous messages from a registrar
(6LR, 6LBR, 6BBR) to indicate that the registration state is removed,
for instance due to time out of a lifetime, or a movement.
The receiver of
the NA is the device that has performed a registration that is now
stale and it should clean up its state.6Duplicate Source Address: The address used as source of the NS(ARO)
conflicts with an existing registration.7Invalid Source Address: The address used as source of the NS(ARO)
is not a Link-Local address as prescribed by this document.8Registered Address topologically incorrect: The address being registered
is not usable on this link, e.g. it is not topologically correct96LBR Registry saturated:
A new registration cannot be accepted because the 6LBR Registry is
saturated.
This code is used by 6LBRs instead of Status 2 when responding to a
DAR/DAC exchange and passed on to the Registering Node by the 6LR.
There is no point for the node to retry this registration immediately
via another 6LR, since the problem is global to the network.
The node may either abandon that address, deregister other addresses
first to make room, or keep the address in TENTATIVE state and retry
later. This specification defines a number of capability bits in the CIO that was
introduced by RFC 7400.
Support for this specification is indicated by setting the "E" flag in
a CIO option.
Routers that are capable of acting as 6LR, 6LBR and 6BBR SHOULD set the L,
B and P flags, respectively.
Those flags are not mutually exclusive and if a router is capable of
multiple roles, it SHOULD set all the related flags.
Option Fields
36 Node is a 6LR, it can take registrations. Node is a 6LBR. Node is a 6BBR, proxying for nodes on this link.
This specification is supported and applied. If the CIO is used in an ND message, then the "E" Flag MUST be set
by the sending node if supports this specification.
It is RECOMMENDED that
a router that supports this specification indicates so with a CIO option,
but this might not be practical if the link-layer MTU is too small.
If the Registering Node receives a CIO in a RA, then the setting of the
E" Flag indicates whether or not this specification is supported.
One alternate way for a 6LN to discover the router's capabilities to first
register a Link Local address, placing the same address in the Source and
Target Address fields of the NS message, and setting the "T" Flag.
The node may for instance register an address that is based on EUI-64.
For such address, DAD is not required and using the SLLAO option in the NS
is actually more amenable with existing ND specifications such as the
"Optimistic Duplicate Address Detection (DAD) for
IPv6".
Once that first registration is complete, the node knows from the setting
of the "T" Flag in the response whether the router supports this specification.
If this is verified, the node may register other addresses that it owns,
or proxy-register addresses on behalf some another node, indicating those
addresses being registered in the Target Address field of the NS messages,
while using one of its own, already registered, addresses as source.
A node that supports this specification MUST always use an EARO as a
replacement to an ARO in its registration to a router.
This is harmless since the "T" flag and TID field are reserved in
RFC 6775 are ignored by a legacy router.
A router that supports this specification answers to an
ARO with an ARO and to an EARO with an EARO.
This specification changes the behavior of the peers in a registration
flows. To enable backward compatibility, a node that registers to a router
that is not known to support this specification MUST behave as prescribed
by RFC 6775. Once the router is known to
support this specification, the node MUST obey this specification.
A legacy 6LN will use the Registered Address as source and will
not use an EARO option. In order to be backward compatible,
an updated 6LR needs to accept that registration if it is valid per the
RFC 6775
specification, and manage the binding cache accordingly.
The main difference with RFC 6775 is that
DAR/DAC exchange for DAD may be avoided for Link-Local addresses.
Additionally, the 6LR SHOULD use an EARO in the reply, and may use any
of the Status codes defined in this specification.
The first registration by a an updated 6LN is for a Link-Local address,
using that Link-Local address as source. A legacy 6LN will not makes
a difference and accept -or reject- that registration as if the 6LN
was a legacy node.
An updated 6LN will always use an EARO option in the registration NS
message, whereas a legacy 6LN will always areply with an ARO option
in the NA message. So from that first registration, the updated 6LN
can figure whether the 6LR supports this specification or not.
When facing a legacy 6LR, an updated 6LN may attempt to find an alternate
6LR that is updated. In order to be backward compatible, based on the
discovery that a 6LR is legacy, the 6LN needs to fallback to legacy
behavior and source the packet with the Registered Address.
The main difference is that the updated 6LN SHOULD use an EARO in the
request regardless of the type of 6LN, legacy or updated
With this specification, the DAR/DAC transports an EARO option as
opposed to an ARO option. As described for the NS/NA exchange,
devices that support this specification always use an EARO option
and all the associated behavior.
This specification extends RFC 6775, and the
security section of that draft also applies to this as well. In particular,
it is expected that the link layer is sufficiently protected to prevent a
rogue access, either by means of physical or IP security on the Backbone
Link and link layer cryptography on the LLN.
This specification also expects that the LLN MAC provides secure unicast
to/from the Backbone Router and secure Broadcast from the Backbone Router
in a way that prevents tempering with or replaying the RA messages.
This specification does not mandate any particular way for forming IPv6
addresses, but it recognizes that use of EUI-64 for forming the Interface
ID in the Link-Local address prevents the usage of
"SEcure Neighbor Discovery (SEND)" and
"Cryptographically Generated Addresses (CGA)",
and that of address privacy techniques, such as recommended in
"Privacy Considerations for IPv6 Adaptation-Layer
Mechanisms".
This specification RECOMMENDS the use of privacy techniques, and that of
additional protection against address theft such as provided by
"Address Protected Neighbor Discovery
for Low-power and Lossy Networks", which guarantees the
ownership of the Registered Address using a cryptographic OUID.
As indicated in section , this protocol does not
aim at limiting the number of IPv6 addresses that a device can form, either.
A host should be able to register any address that is topologically
correct in the subnet(s) advertised by the 6LR/6LBR.
On the other hand, the registration mechanism may be used by a rogue node
to attack the 6LR or the 6LBR with a Denial-of-Service attack against the
registry. It may also happen that the registry of a 6LR or a 6LBR is
saturated and cannot take any more registration, which effectively denies
the requesting a node the capability to use a new address.
In order to alleviate those concerns, provides
a number of recommendations that ensure that a stale registration is
removed as soon as possible from the 6LR and 6LBR.
In particular, this specification recommends that:
A node that ceases to use an address should attempt to deregister that
address from all the 6LRs to which it is registered. The flow is propagated
to the 6LBR when needed, and a sequence number is used to make sure that
only the freshest command is acted upon.
The nodes should be configured with a Registration Lifetime that reflects
their expectation of how long they will use the address with the 6LR to
which it is registered. In particular, use cases that involve mobility or
rapid address changes should use lifetimes that are homogeneous with the
expectation of presence.
The router (6LR or 6LBR) should be configurable so as to limit the number
of addresses that can be registered by a single node, as identified at
least by MAC address and preferably by security credentials. When that
maximum is reached, the router should use a Least-Recently-Used (LRU)
logic so as to clean up the addresses that were not used for the longest
time, keeping at least one Link-Local address, and attempting to keep one
or more stable addresses if such can be recognized, e.g. from the way the
IID is formed or because they are used over a much longer time span than
other (privacy, shorter-lived) addresses.
Administrators should take great care to deploy adequate numbers of 6LR to
cover the needs of the nodes in their range, so as to avoid a situation of
starving nodes. It is expected that the 6LBR that serves a LLN is a more
capable node then the average 6LR, but in a network condition where it may
become saturated, a particular deployment should distribute the 6LBR
functionality, for instance by leveraging a high speed Backbone and
Backbone Routers to aggregate multiple LLNs into a larger subnet.
When the ownership of the OUID cannot be assessed, this specification
limits the cases where the OUID and the TID are multicasted, and
obfuscates them in responses to attempts to take over an address.
The LLN nodes depend on the 6LBR and the 6BBR for their operation.
A trust model must be put in place to ensure that the right devices are
acting in these roles, so as to avoid threats such as black-holing,
or bombing attack whereby an impersonated 6LBR would destroy state in the
network by using the "Removed" Status code.
IANA is requested to create a new subregistry for "ARO Flags"
under the "Internet Control Message Protocol version 6 (ICMPv6) Parameters".
This specification defines 8 positions, bit 0 to bit 7, and assigns bit 7
for the "T" flag in .
The policy is "IETF Review" or "IESG Approval" .
The initial content of the registry is as shown in .
New subregistry for ARO Flags under
the "Internet Control Message Protocol version 6 (ICMPv6) Parameters"ARO StatusDescription Document 0..6Unassigned7"T" FlagRFC ThisIANA is requested to make additions to existing registries as follows:
Address Registration Option Status Values RegistryARO StatusDescription Document 3MovedRFC This4RemovedRFC This5Proof requestedRFC This6Duplicate Source AddressRFC This7Invalid Source AddressRFC This8Registered Address topologically incorrectRFC This96LBR registry saturatedRFC ThisSubregistry for "6LoWPAN capability Bits" under
the "Internet Control Message Protocol version 6 (ICMPv6) Parameters"capability BitDescription Document 116LR capable (L bit)RFC This126LBR capable (B bit)RFC This136BBR capable (P bit)RFC This14EARO support (E bit)RFC ThisKudos to Eric Levy-Abegnoli who designed the First Hop Security infrastructure at Cisco.IEEE Standard for Low-Rate Wireless NetworksIEEE
This specification extends 6LoWPAN ND to sequence the registration and
serves the requirements expressed by enabling the
mobility of devices from one LLN to the next based on the complementary
work in the
"IPv6 Backbone Router"
specification.
In the context of the the TimeSlotted Channel Hopping (TSCH) mode of
IEEE Std. 802.15.4, the
"6TiSCH architecture" introduces how a 6LoWPAN ND host could connect
to the Internet via a RPL mesh Network, but this requires additions to the
6LOWPAN ND protocol to support mobility and reachability in a secured and
manageable environment. This specification details the new operations that
are required to implement the 6TiSCH architecture and serves the
requirements listed in .
The term LLN is used loosely in this specification to cover multiple
types of WLANs and WPANs, including Low-Power Wi-Fi, BLUETOOTH(R) Low Energy,
IEEE Std.802.11AH and IEEE Std.802.15.4 wireless meshes, so as
to address the requirements discussed in This specification can be used by any wireless node to associate at
Layer-3 with a 6BBR and register its IPv6 addresses to obtain routing
services including proxy-ND operations over the Backbone, effectively
providing a solution to the requirements expressed in
.
"Efficiency aware IPv6 Neighbor Discovery Optimizations" suggests
that 6LoWPAN ND can be extended to other types
of links beyond IEEE Std. 802.15.4 for which it was defined.
The registration technique is beneficial when the Link-Layer technique
used to carry IPv6 multicast packets is not sufficiently efficient in
terms of delivery ratio or energy consumption in the end devices, in
particular to enable energy-constrained sleeping nodes.
The value of such extension is especially apparent in the case of mobile
wireless nodes, to reduce the multicast operations that are related
to classical ND (, ) and
plague the wireless medium. This serves scalability requirements listed
in .
This section lists requirements that were discussed at 6lo for an update
to 6LoWPAN ND. This specification meets most of them, but those listed in
which are deferred to a different specification such as
, and those related to multicast.
Due to the unstable nature of LLN links, even in a LLN of immobile nodes
a 6LN may change its point of attachment to a 6LR, say 6LR-a,
and may not be able to notify 6LR-a. Consequently, 6LR-a may still attract
traffic that it cannot deliver any more. When links to a 6LR change state,
there is thus a need to identify stale states in a 6LR and restore
reachability in a timely fashion.
Req1.1: Upon a change of point of attachment, connectivity via a new 6LR MUST be
restored timely without the need to de-register from the previous 6LR.
Req1.2: For that purpose, the protocol MUST enable to differentiate between multiple
registrations from one 6LoWPAN Node and registrations from different 6LoWPAN Nodes
claiming the same address.
Req1.3: Stale states MUST be cleaned up in 6LRs.
Req1.4: A 6LoWPAN Node SHOULD also be capable to register its Address to multiple
6LRs, and this, concurrently.
The point of attachment of a 6LN may be a 6LR in an LLN mesh.
IPv6 routing in a LLN can be based on RPL, which is the routing
protocol that was defined at the IETF for this particular purpose.
Other routing protocols than RPL are also considered by Standard Defining
Organizations (SDO) on the basis of the expected network characteristics.
It is required that
a 6LoWPAN Node attached via ND to a 6LR would need to participate in the
selected routing protocol to obtain reachability via the 6LR.
Next to the 6LBR unicast address registered by ND, other addresses including
multicast addresses are needed as well. For example a routing protocol often
uses a multicast address to register changes to established paths.
ND needs to register such a multicast address to enable routing concurrently
with discovery.
Multicast is needed for groups. Groups MAY be
formed by device type (e.g. routers, street lamps), location (Geography,
RPL sub-tree), or both.
The Bit Index Explicit Replication (BIER)
Architecture
proposes an optimized technique to enable multicast in a LLN with a very
limited requirement for routing state in the nodes.
Related requirements are:
Req2.1: The ND registration method SHOULD be extended in such a fashion that
the 6LR MAY advertise the Address of a 6LoWPAN Node over the selected routing
protocol and obtain
reachability to that Address using the selected routing protocol.
Req2.2: Considering RPL, the Address Registration Option that is used in
the ND registration
SHOULD be extended to carry enough information to generate a DAO
message as specified in section 6.4, in particular
the capability to compute a Path Sequence and, as an option, a RPLInstanceID.
Req2.3: Multicast operations SHOULD be supported and optimized, for instance
using BIER or MPL. Whether ND is appropriate for the registration to the 6BBR
is to be defined, considering the additional burden of supporting the
Multicast Listener Discovery Version 2
(MLDv2) for IPv6.
6LoWPAN ND was defined with a focus on
IEEE Std.802.15.4 and in particular the capability to derive a unique Identifier
from a globally unique MAC-64 address. At this point, the 6lo Working
Group is extending the 6LoWPAN Header Compression (HC)
technique to other link types
ITU-T G.9959,
Master-Slave/Token-Passing,
DECT Ultra Low Energy,
Near Field Communication,
IEEE Std. 802.11ah,
as well as
IEEE1901.2 Narrowband Powerline Communication Networks and
BLUETOOTH(R) Low Energy.
Related requirements are:
Req3.1: The support of the registration mechanism SHOULD be extended to more LLN
links than IEEE Std.802.15.4, matching at least the LLN links for which an "IPv6
over foo" specification exists, as well as Low-Power Wi-Fi.
Req3.2: As part of this extension, a mechanism to compute a unique Identifier should
be provided, with the capability to form a Link-Local Address that SHOULD be unique at least within the LLN connected to a 6LBR discovered by ND in each node within the LLN.
Req3.3: The Address Registration Option used in the ND registration SHOULD be
extended to carry the relevant forms of unique Identifier.
Req3.4: The Neighbour Discovery should specify the formation of a site-local address that follows the security recommendations from .
Duty-cycled devices may not be able to answer themselves to a lookup from a node
that uses classical ND on a Backbone and may need a proxy. Additionally, the duty-cycled device may need to rely on the 6LBR to perform
registration to the 6BBR.
The ND registration method SHOULD defend the addresses of duty-cycled devices that are sleeping most of the
time and not capable to defend their own Addresses.
Related requirements are:
Req4.1: The registration mechanism SHOULD enable a third party to proxy register
an Address on behalf of a 6LoWPAN node that may be sleeping or located
deeper in an LLN mesh.
Req4.2: The registration mechanism SHOULD be applicable to a duty-cycled device
regardless of the link type, and enable a 6BBR to operate as a proxy to
defend the Registered Addresses on its behalf.
Req4.3: The registration mechanism SHOULD enable long sleep durations, in the
order of multiple days to a month.
In order to guarantee the operations of the 6LoWPAN ND flows, the
spoofing of the 6LR, 6LBR and 6BBRs roles should be avoided. Once a node
successfully registers an address, 6LoWPAN ND should provide energy-efficient
means for the 6LBR to protect that ownership even when the node that registered the address is sleeping.
In particular,
the 6LR and the 6LBR then should be able to verify whether a subsequent
registration for a given Address comes from the original node.
In a LLN it makes sense to base security on layer-2 security. During bootstrap of the LLN, nodes join the network after authorization by a Joining Assistant (JA) or a Commissioning Tool (CT). After joining nodes communicate with each other via secured links. The keys for the layer-2 security are distributed by the JA/CT. The JA/CT can be part of the LLN or be outside the LLN. In both cases it is needed that packets are routed between JA/CT and the joining node.
Related requirements are:
Req5.1: 6LoWPAN ND security mechanisms SHOULD provide a mechanism for the
6LR, 6LBR and 6BBR to authenticate and authorize one another for their
respective roles, as well as with the 6LoWPAN Node for the role of 6LR.
Req5.2: 6LoWPAN ND security mechanisms SHOULD provide a mechanism for the 6LR
and the 6LBR to validate new registration of authorized nodes.
Joining of unauthorized nodes MUST be impossible.
Req5.3: 6LoWPAN ND security mechanisms SHOULD lead to small packet sizes. In
particular, the NS, NA, DAR and DAC messages for a re-registration flow
SHOULD NOT exceed 80 octets so as to fit in a secured IEEE Std.802.15.4
frame.
Req5.4: Recurrent 6LoWPAN ND security operations MUST NOT be computationally
intensive on the LoWPAN Node CPU. When a Key hash calculation is employed, a
mechanism lighter than SHA-1 SHOULD be preferred.
Req5.5: The number of Keys that the 6LoWPAN Node needs to manipulate SHOULD
be minimized.
Req5.6: The 6LoWPAN ND security mechanisms SHOULD enable the variation of CCM
called CCM* for use at both
Layer 2 and Layer 3, and SHOULD enable the reuse of security code that has to
be present on the device for upper layer security such as TLS.
Req5.7: Public key and signature sizes SHOULD be minimized while maintaining
adequate confidentiality and data origin authentication for multiple types
of applications with various degrees of criticality.
Req5.8: Routing of packets should continue when links pass from the unsecured
to the secured state.
Req5.9: 6LoWPAN ND security mechanisms SHOULD provide a mechanism for the 6LR
and the 6LBR to validate whether a new registration for a given address
corresponds to the same 6LoWPAN Node that registered it initially, and,
if not, determine the rightful owner, and deny or clean-up
the registration that is duplicate.
Use cases from Automatic Meter Reading (AMR, collection tree operations) and
Advanced Metering Infrastructure (AMI, bi-directional communication to the
meters) indicate the needs for a large number of LLN nodes pertaining to a
single RPL DODAG (e.g. 5000) and connected to the 6LBR over a large number of
LLN hops (e.g. 15).
Related requirements are:
Req6.1: The registration mechanism SHOULD enable a single 6LBR to register
multiple thousands of devices.
Req6.2: The timing of the registration operation should allow for a large
latency such as found in LLNs with ten and more hops.